Viscoelastic composition

ABSTRACT

The purpose of the present invention is to provide a viscoelastic composition having excellent operability, which is suitable for use in securing the field of view of an endoscope when opaque dark-colored liquid accumulates inside a canal and obstructs the field of view of the endoscope, the viscoelastic composition securing the field of view by pushing the liquid aside, and to provide a method for securing the field of view of an endoscope using the viscoelastic composition. The viscoelastic composition for securing the field of view of an endoscope comprises a substance having viscoelastic properties and water, preferably has a hardness of 550 N/m 2  or less, a viscosity (25° C.) of 200 to 2,000 mPa·s, and a loss tangent of 0.6 or less, and more preferably has an electrical conductivity of 250 μS/cm or less. The method for securing the field of view of an endoscope comprises feeding the viscoelastic composition from a proximal part of the endoscope, through a channel, into a distal part of the endoscope.

TECHNICAL FIELD

The present invention relates to a viscoelastic composition suitable foruse in securing the field of view of an endoscope, and a method forsecuring the field of view of an endoscope using the viscoelasticcomposition. More particularly, the invention relates to theviscoelastic composition having excellent operability, which is suitablefor use in securing the field of view of an endoscope when opaquedark-colored liquid accumulates inside a canal and obstructs the fieldof view of the endoscope, the viscoelastic composition securing thefield of view by pushing the liquid aside, and also relates to a methodfor securing the field of view of an endoscope using the viscoelasticcomposition.

BACKGROUND ART

Endoscopes may be used to observe the interior of a fine canal such asan alimentary canal or a bile duct. However, if dark-colored liquid thatwould block light, such as blood, intestinal juice or bile, or asemi-solid material such as food residue or excrement accumulates in theinterior of a canal, the field of view of an endoscope is obstructed,and the interior state of the canal cannot be fully observed. In thesecircumstances, the field of view of an endoscope has been hithertosecured by conveying water or gas into the interior of the canal.Conveying water means a method of injecting water such as tap water intothe canal and washing away the liquid or the semi-solid material insidethe canal. The field of view is temporarily secured in the method byremoving the liquid or the semi-solid material inside the canal;however, in many cases, the liquid or the semi-solid material thusremoved is mixed with tap water or the like, opaque liquid thussuspended diffuses in the canal, and securing the field of view is stilldifficult. On the other hand, conveying gas means a method of blowingair into the interior of the canal thereby removing the liquid or thesemi-solid material in the canal. The field of view is also temporarilysecured in the method by removing the liquid or the semi-solid materialinside the canal; however, when there is a hemorrhage site, removingblood is difficult, and the field of view is not secured. Therefore,there have been problems associated with difficulties in identifying ahemorrhage site and operating for a hemostasis treatment. Therefore,there has been an urgent necessity in developing a method for securingthe field of view of an endoscope with excellent operability.

Patent Literature 1 discloses a method of treating urinary incontinence,rectal incontinence, vesicoureteral reflux, or the like by injecting ahydrogel consisting of crosslinked polymers into the urethra or therectum.

Patent Literature 2 discloses a hydrogel composition comprising apolysaccharide, synthetic polymer, and crosslinking agent. It seems thatthis hydrogel composition is crosslinked and cured with a buffersolution and becomes a sticky hydrogel.

Patent Literature 3 discloses a method of inflating a body cavity suchas the uterus by filling the body cavity with a physiological fluid suchas physiological saline or lactated Ringer's solution so as to treat theinterior of the body cavity.

CITATION LIST Patent Literatures

-   Patent Literature 1: JP 2007-506463 A-   Patent Literature 2: JP 2013-510175 A-   Patent Literature 3: JP 2000-513970 A

SUMMARY OF INVENTION Technical Problem

The problem of the present invention is to provide a viscoelasticcomposition having excellent operability, which is suitable for use insecuring the field of view of an endoscope when opaque dark-coloredliquid accumulates inside a canal and obstructs the field of view of theendoscope, the viscoelastic composition securing the field of view bypushing the liquid aside, and to provide a method for securing the fieldof view of an endoscope using the viscoelastic composition. The problemdesirably includes providing the viscoelastic composition that makes itpossible to assist a simplified hemostasis treatment.

Solution to Problem

The inventors of the present invention conducted intensive studies inorder to solve the aforementioned problems, and as a result, theinventors found that the use of a viscoelastic composition havingelasticity together with viscosity is useful, and that particularly bydefining the following physical properties: hardness, viscosity, andloss tangent, the composition exhibits excellent operability when usedwith an endoscope with securing the satisfactory field of view. Thus,the inventors finally completed the present invention as describedbelow. Further, the inventors also found that by adjusting theelectrical conductivity of the viscoelastic composition, assistance of asimplified hemostasis treatment is possible with securing thesatisfactory field of view.

(1) A viscoelastic composition for securing the field of view of anendoscope, the viscoelastic composition comprising a thickeningsubstance and water.

(2) The viscoelastic composition according to (1), wherein theviscoelastic composition has a hardness of 550 N/m² or less, a viscosityat 25° C. of 200 to 2,000 mPa·s, and a loss tangent of 0.6 or less.

(3) The viscoelastic composition according to (2), wherein theviscoelastic composition further has an electrical conductivity of 250μS/cm or less.

(4) A method for securing the field of view of an endoscope, the methodcomprising feeding the viscoelastic composition according to any one of(1) to (3) from a proximal part of the endoscope, through a channel,into a distal part of the endoscope.

(5) The method according to (4), wherein the endoscope is a medicalendoscope.

Advantageous Effects of Invention

The viscoelastic composition of the present invention is both viscousand elastic, and due to the viscoelasticity, the viscoelasticcomposition is capable of physically pushing aside liquid such as blood,intestinal juice or bile, or a semi-solid material such as food residueor excrement. Further, since the viscoelastic composition of the presentinvention does not easily mix with the aforementioned liquid orsemi-solid material, suspension does not occur. Furthermore, since theviscoelastic composition of the present invention has adequateconsistency, diffusion does not occur thereby making it possible tosecure a satisfactory field of view. Moreover, the viscoelasticcomposition of the present invention may have a reduced electricalconductivity by including no material having electrical charge or byincluding a minimal amount of the material, thereby making it possibleto assist hemostasis treatments by means of electroscission,electrocoagulation, etc., while securing the field of view in thepresence of the viscoelastic composition.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a photograph of a proximal part of a medicalendoscope.

FIG. 2A is a conceptual diagram illustrating the state of the interiorof an alimentary canal that has hemorrhaged.

FIG. 2B is a conceptual diagram illustrating the state in which waterhas been injected into the hemorrhaged alimentary canal.

FIG. 3A is a conceptual diagram illustrating the state of the interiorof an alimentary canal that has hemorrhaged.

FIG. 3B is a conceptual diagram illustrating the state in which theviscoelastic composition of the present invention has been injected intothe hemorrhaged alimentary canal.

FIG. 4A is a diagram illustrating a method of evaluation from theviewpoint of securing the field of view when a viscoelastic compositionis used for endoscopy.

FIG. 4B is a diagram illustrating a method of evaluation from theviewpoint of securing the field of view when the viscoelasticcomposition is used for endoscopy.

FIG. 5A is a diagram illustrating a method of evaluation from theviewpoint of securing the field of view when a viscoelastic compositionis used for endoscopy.

FIG. 5B is a diagram illustrating a method of evaluation from theviewpoint of securing the field of view when the viscoelasticcomposition is used for endoscopy.

FIG. 6 is a graph showing the relation between the viscosity and losstangent of the viscoelastic composition and the success or failure insecuring the field of view when the viscoelastic composition is used forendoscopy.

FIG. 7 is a graph showing the relation between the viscosity andhardness of the viscoelastic composition and the suitability orunsuitability in operability when the viscoelastic composition is usedfor endoscopy.

FIG. 8 is a graph showing the relation between the hardness and losstangent of the viscoelastic composition and the success or failure insecuring the field of view and suitability or unsuitability inoperability when the viscoelastic composition is used for endoscopy.

FIG. 9 is a diagram illustrating an example of camera images obtainedwhen water is injected from the forceps of an endoscope.

FIG. 10 is a diagram illustrating an example of camera images obtainedwhen the viscoelastic composition is injected from the forceps of anendoscope.

FIG. 11 is a diagram illustrating the result of a thermocoagulationtreatment using a high-frequency current, the treatment simulating atreatment with an endoscope.

FIG. 12 is a diagram illustrating the result of the thermocoagulationtreatment using a high-frequency current, the treatment simulating thetreatment with the endoscope.

FIG. 13 is a diagram illustrating the result of the thermocoagulationtreatment using a high-frequency current, the treatment simulating thetreatment with the endoscope.

FIG. 14 is a diagram illustrating the result of the thermocoagulationtreatment using a high-frequency current, the treatment simulating thetreatment with the endoscope.

FIG. 15 is a diagram illustrating the result of the thermocoagulationtreatment using a high-frequency current, the treatment simulating thetreatment with the endoscope.

FIG. 16 is a diagram illustrating the result of a thermocoagulationtreatment using a high-frequency current, the treatment simulating thetreatment with the endoscope.

FIG. 17 is a diagram illustrating the result of a thermocoagulationtreatment using a high-frequency current, the treatment simulating thetreatment with the endoscope.

DESCRIPTION OF EMBODIMENTS

The viscoelastic composition of the present invention comprises athickening substance and water.

The viscoelastic composition of the present invention may be prepared bycombining one or more kinds of thickening substances having a propertyof increasing viscosity when dispersed in water. Examples of suchthickening substances include alcohols such as methanol, ethanol,2-propanol, 1,4-butanediol, 1,3-butylene glycol, propylene glycol,glycerin catechin, glucose, fructose, galactose, sucrose, lactose,maltose, trehalose, xylitol, sorbitol, mannitol, glucosamine, andgalactosamine; polysaccharides such as Aureobasidium culture solution,flaxseed gum, gum Arabic, arabinogalactan, alginic acid and saltsthereof, propylene glycol alginate ester, welan gum, Cassia gum, gumghatti, curdlan, carrageenan, karaya gum, xanthan gum, guar gum, guargum enzymolysis products, psyllium seed gum, Artemisia sphaerocephalaseed gum, gellan gum, succinoglycan, tamarind gum, tara gum, dextran,tragacanth gum, furcellaran, funoran, pullulan, pectin, macrophomopsisgum, Rhamsan gum, levan, locust bean gum, starch grafted acrylate,acetylated distarch adipate, acetylated oxidized starch, acetylateddistarch phosphate, starch sodium octenylsuccinate, carboxymethylcellulose and salts thereof, carboxymethyl ethyl cellulose, starchacetate, oxidized starch, sodium starch glycolate, hydroxypropyldistarch phosphate, hydroxypropyl cellulose, hydroxypropyl starch,hydroxypropyl methyl cellulose, hydroxymethyl cellulose, hydroxyethylmethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, methylcellulose, cellulose, distarch phosphate, monostarch phosphate,phosphateddistarch phosphate, fucoidan, diutan gum, glucomannan,hyaluronic acid and salts thereof, keratan sulfate, heparin, chondroitinsulfate, dermatan sulfate, scleroglucan, schizophyllan, okra extracts,Krantz aloe extracts, sesbania gum, agarose, agaropectin, amylose,amylopectin, pregelatinized starch, inulin, levan graminan, agar,hydroxypropyl methylcellulose stearoxy ether, sodium starch glycolate,dextran, dextrin, croscarmellose sodium, glucuronoxylan, andarabinoxylan; proteins such as gelatin, hydrolyzed gelatin, andcollagen; polyamino acids such as polyglutamic acid, polylysine, andpolyaspartic acid; hydrophilic polymers such as a carboxyvinyl polymer,polyacrylic acid and salts thereof, a partially neutralized polyacrylicacid, polyvinyl alcohol, a polyvinyl alcohol-polyethylene glycol graftcopolymer, polyethylene glycol, polypropylene glycol, and polybutyleneglycol; and metal salts such as calcium chloride, aluminum hydroxide,magnesium chloride, and copper sulfate.

The water used in the viscoelastic composition of the present inventionis not particularly limited, but preferably is softened water, purewater, deionized water, distilled water, or a physiological aqueoussolution such as physiological saline, Ringer's solution, or acetatedRinger's solution.

The viscoelastic composition of the present invention may comprise oneor more additives such as a preservative or an antiseptic agent.

The problem of the present invention is to provide a viscoelasticcomposition having excellent operability and capable of securing asatisfactory field of view, and desirably, to provide a viscoelasticcomposition that also makes it possible to assist a simplifiedhemostasis treatment. Among these problems, the obstruction of the fieldof view of an endoscope is considered to be caused by liquid such asblood, intestinal juice or bile, or a semi-solid material such as foodresidue or excrement that: 1) accumulates inside a canal lumen; 2) mixeswith water and thereby impairing transparency; and/or 3) flows ordiffuses by water conveyance. In order to secure the satisfactory fieldof view, a transparent composition having viscoelasticity that isdifferent from that of liquid such as blood, intestinal juice or bile,or a semi-solid material such as excrement may be injected into thelumen, thereby physically pushing aside and removing these materials andthen securing a space. Also, the transparent composition is not easilymixed with the liquid such as blood, intestinal juice or bile, or thesemi-solid material such as excrement, and thus may suppress flowing ordiffusion of the liquid. On the other hand, the problem of havingexcellent operability means that the viscoelastic composition can passthrough a forceps opening of an endoscope without excessive resistance.The problem of making it possible to assist a simplified hemostasistreatment means that a hemorrhage site can be recognized in the presenceof the viscoelastic composition, and an assistance of a hemostasistreatment using a high-frequency current is made possible.

The viscoelastic composition of the present invention preferably has ahardness of 550 N/m² or less, and more preferably 400 N/m² or less, aviscosity (25° C.) of 200 to 2,000 mPa·s, and more preferably 500 to1,500 mPa·s, and a loss tangent of 0.6 or less.

When the hardness is adjusted to the range described above, satisfactoryoperability is achieved when the composition is injected through theforceps of an endoscope. Furthermore, when the viscosity and losstangent are adjusted to the ranges described above, improvements aremade from the viewpoint of securing the field of view. Further, alsofrom the viewpoint of securing the field of view, the viscoelasticcomposition may be made transparent.

The viscoelastic composition of the present invention preferably has anelectrical conductivity of 250 μS/cm or less, and more preferably 200μS/cm or less.

When the electrical conductivity is adjusted to the range describedabove, a viscoelastic composition is obtainable that may be excellent inthermocoagulation hemostasis and is particularly suitable for treatmentssuch as electroscission or electrocoagulation.

The viscoelastic composition of the present invention may be obtained bymixing one or more thickening substances such as those described abovewith water, and specifically, the viscoelastic composition may beobtained by, e.g., combining two or more kinds of thickening substances,or dissolving one kind of a thickening substance in water or the like,followed by subjecting the resultant to a heating treatment therebyimparting elasticity to the product. When there are bubbles in theviscoelastic composition of the present invention, the field of view isobstructed; therefore, it is preferable that the viscoelasticcomposition substantially includes no bubbles.

A method for securing the field of view of an endoscope of the presentinvention comprises feeding the viscoelastic composition of the presentinvention from a proximal part of the endoscope, through a channel, intoa distal part of the endoscope.

FIG. 1 is a diagram showing a photograph of a proximal part of a medicalendoscope as a representative example of endoscopes. The proximal partincludes a dial 11 for performing an angle manipulation; a scopeconnector unit 12 for transmitting light from a light source apparatusand transmitting the information of images to an electronic endoscopeprocessor; and a forceps opening 15 through which a treatment tool suchas forceps is inserted and conveyed to the distal part 1. A channel thatconnects through from the forceps opening to the distal part, a waterconveying duct for washing the lens in the distal part with water, anoptical system and the like are provided inside an endoscope flexibletube 17. A forceps lid 16 is provided at the forceps opening 15 of themedical endoscope illustrated in FIG. 1. One end of a tube 13 isconnected to the forceps lid 16, and the other end of the tube isconnected to a connector 14 which is to be mounted to a syringe or thelike. The forceps lid 16 is provided inside with a valve body, one endof the tube 13 is opened toward a wall surface of the valve body insidethe forceps lid 16, the wall surface being on the side of the forcepsopening 15, so that even when a treatment tool such as forceps isinserted, the liquid that has been injected through the tube isprevented from flowing out due to the valve body (see, for example, JP2014-155677 A).

EXAMPLES Reference Example

An endoscope may be inserted into an alimentary canal such as therectum, thereby making it possible to observe the inside of thealimentary canal using the endoscope. When hemorrhage occurs in analimentary canal 4, blood 3 accumulates inside the alimentary canal, anda hemorrhage site 2 cannot be observed (FIG. 2A). In such circumstances,the accumulated blood was attempted to be washed away with water byfilling a syringe with tap water and injecting the water by the syringethrough a tube 13, a forceps opening 15, and a channel to the opening ofthe endoscope distal part 1, through which the water was injected intothe alimentary canal. However, the injected water was mixed andsuspended with the accumulated blood and thus the water became turbidwater 3″. When the turbid water 3″ accumulates inside the alimentarycanal, the field of view of the endoscope is obstructed by the turbidwater 3″, and thus the hemorrhage site 2 cannot be observed. A surgicaloperation cannot be continued accordingly (FIG. 2B and FIG. 9).

In contrast, with regard to the viscoelastic composition of the presentinvention, when there is a hemorrhage site 2 in an alimentary canal 4,the blood 3 that has accumulated inside the alimentary canal may bepushed aside (blood 3′) by injecting the viscoelastic composition fromthe distal part of the endoscope as illustrated in FIG. 3A and FIG. 3B.The viscoelastic composition of the present invention thus makes itpossible to observe the hemorrhage site 2.

Examples and Comparative Examples

In the present Examples or Comparative Examples, the relation betweenthe viscoelastic properties of viscoelastic compositions used forendoscopy and the securement of the field of view and the operability inoperating an endoscope was investigated.

Methods for determining the physical properties of viscoelasticcompositions and methods for evaluating the viscoelastic compositionsfrom the viewpoint of securing the field of view and from the viewpointof operability when used for endoscopy are shown below.

(1) Viscosity and Loss Tangent

Viscosity and viscoelasticity are determined using HAAKE RS-6000 (ThermoFisher Scientific, Inc.). A viscoelastic composition was mounted on asample stand, and measurements were made using P35 Ti L parallel plates(measurement conditions: temperature 25° C., gap 1.000 mm, stress 1,000mPa, and frequency 0.5000 Hz). The values obtained after 30 minutes fromthe initiation of measurement were measured.

(2) Hardness

Hardness is determined using a creepmeter, Model RE2-33005C (YAMADENCo., Ltd.). A stainless steel Petri dish (outer diameter: 45 mm, innerdiameter: 41 mm, external dimension: 18 mm, and internal dimension: 15mm) was filled with a viscoelastic composition, the height of theviscoelastic composition was aligned with the height of the Petri dish,and the surface of the specimen was made flat. Measurements were madeusing a plunger (YAMADEN Co., Ltd., shape: disc, model: P-56, remarks:ϕ20×t 8) (measurement conditions: storage pitch 0.02 sec, measurementdistortion rate 66.67%, measurement speed 10 mm/sec, return distance5.00 mm, sample thickness 15.00 mm, contact surface diameter 20.00 mm,and contact area 0.000 mm²).

(3) Electrical Conductivity

Electrical conductivity was determined using an electrical conductivitymeter CM-41X (DKK-TOA CORPORATION) and a CT-57101C cell for lowelectrical conductivity measurement (measurement conditions: temperature25° C.).

(4) Method for Evaluation in Securing the Field of View

3 mL of a 1% Evans Blue solution (dye solution) was injected into aDean-Stark trap, and a catheter tube attached with a wire was insertedthereto. In this state, the field of view is obstructed by the dyesolution, and the wire at the tip of the tube is not visible (FIG. 4Aand FIG. 5A). Each 10 mL of viscous compositions having different losstangent, hardness and viscosity was injected into the dye solutionthrough the catheter tube (inner diameter: 2.5 to 3 mm, and length:1.000 mm), and success or failure in securing the field of view wasdetermined by visual inspection. When a certain viscous composition Awas injected, a physical space was secured, and the viscous compositionA was not easily mixed with the dye solution. In this case, the viscouscomposition A was considered to exhibit desired viscoelastic properties,and thus was concluded to be “acceptable” as the viscoelasticcomposition (FIG. 4B). On the other hand, when a viscous composition Bdifferent from the viscous composition A was injected, whether aphysical space was secured or not was obscure, and the viscouscomposition B was mixed with the dye solution. In this case, the viscouscomposition B was not considered to exhibit desired viscoelasticproperties, and thus was concluded to be “unacceptable” as theviscoelastic composition (FIG. 5B).

The results obtained from the evaluation in securing the field of viewcorrespond to the occurrence of differences in providing the field ofview as shown in, for example, FIG. 9 and FIG. 10. That is, when anendoscope was inserted to a hemorrhage site and water was injectedthereinto, the field of view obtained from a camera was not satisfactorydue to turbid water as illustrated in FIG. 9. In contrast, when anendoscope was inserted to a hemorrhage site and a viscoelasticcomposition exhibiting desired viscoelastic properties was injectedthereinto, the hemorrhage site 2 was clearly detected in the field ofview obtained from a camera as illustrated in FIG. 10.

(5) Method for Evaluation in Operability

Since a viscoelastic composition used for securing the field of view isinjected into an alimentary canal through a forceps opening (innerdiameter: 2.8 to 3.8 mm) of an endoscope, the viscoelastic compositionmay desirably be injected smoothly without any excessive resistance.Each of the viscoelastic compositions having different loss tangent,hardness and viscosity was filled into a 50-mL syringe (JMS Co., Ltd.)and then a catheter tube (inner diameter: 3 mm, and length: 1.000 mm)simulating the inner diameter of a forceps opening of the endoscope wasmounted to the tip of the syringe. The passability of the viscoelasticcompositions was then subjectively determined. Viscoelastic compositionsthat passed smoothly or passed with slight resistance at a practicallyacceptable level were concluded to be “suitable”. In contrast,viscoelastic compositions that exhibited too excessive resistance toendure practical uses or exhibited too excessive resistance to passthrough the tube were concluded to be “unsuitable”.

Test Example 1: As to the Relation Between Loss Tangent, Hardness, andViscosity of Viscoelastic Compositions

Viscoelastic compositions having different loss tangent, hardness andviscosity were prepared and tested for the securement of the field ofview and operability, and then the relation thereof with variousphysical properties was evaluated. All the loss tangents of theviscoelastic compositions that were concluded to be “acceptable” insecuring the field of view were about 0.6 or less, whereas all theviscoelastic compositions having a higher loss tangent were concluded tobe “unacceptable” (FIG. 6). The viscoelastic compositions that wereconcluded to be “suitable” in operability had a hardness of about 550N/m² or less and a viscosity of about 2,000 mPa·s or less, whereas allthe viscoelastic compositions having a higher hardness or viscosity wereconcluded to be “unsuitable” (FIG. 7). The loss tangent and hardness ofthe viscoelastic compositions that satisfied both the “acceptable” insecuring the field of view and the “suitable” in operability are thesame as those described above (FIG. 8). It was found from theseexperimental examples that a viscoelastic composition having a losstangent of 0.6 or less, a hardness of 550 N/cm² or less, and a viscosityof 200 to 2,000 mPa·s is preferable in order to achieve the excellentproperties in securing the field of view and operability in endoscopictreatments.

Test Example 2: As to the Electrical Conductivity of ViscoelasticCompositions

There are three methods for endoscopic hemostasis; a method based onthermocoagulation using a high frequency-current, a method using a clip,and a method using one or more medicines. In a thermocoagulation method,a high-frequency current is passed through a hemorrhage site, andtissues are coagulated and stanched by means of the heat generatedconcentratedly at the hemorrhage site. In this instance, generally, if asolution or a substance having high electrical conductivity exists inthe vicinity of the hemorrhage site, the high-frequency current wouldleak, and satisfactory thermocoagulation could not be achieved.

Based on the knowledge, treatments and evaluation were performedaccording to the following procedure.

A small tube (diameter: about 1.5 cm) was compressively bonded to thesurface of the liver of a rat, and the interior of the tube was filledwith physiological saline, distilled water, or viscoelastic compositionsthat had been prepared to have different electrical conductivities. Thetip of a unipolar electrode (Edge-coated blade electrode E1450X) wassoftly pressed against the liver surface, and electricity was passed for2 seconds in the coagulation mode (SURGISTAT II, Covidien Japan, Inc.,set to a coagulation output of 20). Satisfactory thermocoagulation wasobserved in a gas phase (FIG. 11) and in tap water having a lowelectrical conductivity (FIG. 12); however, unsatisfactorythermocoagulation was observed in physiological saline having a highelectrical conductivity (FIG. 13). Further, satisfactorythermocoagulation was observed in viscoelastic compositions having anelectrical conductivity of 12.8 mS/m (128 μS/cm) or less (FIG. 14 andFIG. 15), and thermocoagulation to the extent that it had no problem forpractical uses was observed in a viscoelastic composition having anelectrical conductivity of 25 mS/m (250 μS/cm) or less, for example,22.4 mS/m (224 μS/cm) or less (FIG. 16). However, unsatisfactorythermocoagulation was observed in a viscoelastic composition having ahigh electrical conductivity, for example, 60.8 mS/m (608 μS/cm) (FIG.17). It was found from these experimental examples that a viscoelasticcomposition which is excellent in securing the field of view andoperability in endoscopic treatments should have an electricalconductivity of preferably 25 mS/m or less, and more preferably 20 mS/mor less in consideration of thermocoagulation hemostasis using ahigh-frequency current. The results are also shown in the followingTable 1.

TABLE 1 Electrical conductivity of viscoelastic compositions(thermocoagulation) Electrical conductivity Material (mS/m)Thermocoagulation* 2-1 Gas phase — E 2-2 Tap water 10 E 2-3Physiological 1600 NG saline 2-4 Viscoelastic 1.8 E composition 2-5Viscoelastic 12.8 E composition 2-6 Viscoelastic 22.4 G composition 2-7Viscoelastic 60.8 NG composition *E: Excellent (satisfactorythermocoagulation was observed) G: Good (thermocoagulation was observed)NG: Not Good (thermocoagulation was insufficient)

In the following Table 2, viscoelastic compositions that were concludedto be “suitable” in operability in endoscopic treatments and werecapable of realizing thermocoagulation using a high-frequency currentare shown, and about the respective viscoelastic compositions, successor failure in securing the field of view is also shown.

TABLE 2 Concentration Viscosity Loss Hardness Securement of theViscoelastic composition (wt %) Ratio (mPa · s) tangent (N/m²) field ofview Operability Xanthan gum: Locust bean 0.08 4:6 1012 0.11 360Acceptable Suitable gum 0.08 8:2 123 0.69 180 Unacceptable Suitable 0.128:2 230 0.56 241 Acceptable Suitable 0.20 2:8 3597 0.58 596 AcceptableUnsuitable Tamarind gum: Sucrose 11.0  1:10 97 104.7 134 UnacceptableSuitable Tamarind gum: D-mannitol 11.0  1:10 110 9.36 134 UnacceptableSuitable Tamarind gum: Glycerin 11.0  1:20 89 69.83 131 UnacceptableSuitable Carrageenan: Locust bean gum 0.10 6:4 13 4.03 125 UnacceptableSuitable Hypromellose 8.00 — 581 140 153 Unacceptable Suitable Sodiumcarboxymethyl 1.50 — 1112 1.34 215 Unacceptable Suitable celluloseXanthan gum: Tara gum 0.40 7:3 1863 0.28 539 Acceptable Suitable 0.107:3 101 1.00 150 Unacceptable Suitable Sodium alginate/Calcium 2.73/0.16— 1858 0.43 395 Acceptable Suitable chloride

REFERENCE SIGNS LIST

-   -   1 Endoscope distal portion    -   2 Hemorrhage site    -   3, 3′ Blood    -   3″ Turbid water    -   11 Dial    -   12 Scope connector unit    -   13 Tube    -   14 Connector    -   15 Forceps opening    -   16 Forceps lid    -   17 Endoscope flexible tube

What is claimed is:
 1. A viscoelastic composition for securing the fieldof view of an endoscope, the viscoelastic composition comprising athickening substance and water and having a loss tangent of 0.6 or less.2. The viscoelastic composition according to claim 1, wherein theviscoelastic composition has a hardness of 550 N/m2 or less, a viscosityat 25° C. of 200 to 2,000 mPa·s, and a loss tangent of 0.6 or less. 3.The viscoelastic composition according to claim 2, wherein theviscoelastic composition further has an electrical conductivity of 250μS/cm or less.
 4. A method for securing the field of view of anendoscope, the method comprising feeding the viscoelastic compositionaccording to claim 1 from a proximal part of the endoscope, through achannel, into a distal part of the endoscope.
 5. The method according toclaim 4, wherein the endoscope is a medical endoscope.
 6. A viscoelasticcomposition for securing the field of view of an endoscope, theviscoelastic composition comprising a thickening substance and water andhaving an electrical conductivity of 250 μS/cm or less.
 7. A method forsecuring the field of view of an endoscope, the method comprisingfeeding the viscoelastic composition according to claim 2 from aproximal part of the endoscope, through a channel, into a distal part ofthe endoscope.
 8. The method according to claim 7, wherein the endoscopeis a medical endoscope.
 9. A method for securing the field of view of anendoscope, the method comprising feeding the viscoelastic compositionaccording to claim 3 from a proximal part of the endoscope, through achannel, into a distal part of the endoscope.
 10. The method accordingto claim 9, wherein the endoscope is a medical endoscope.
 11. A methodfor securing the field of view of an endoscope, the method comprisingfeeding the viscoelastic composition according to claim 6 from aproximal part of the endoscope, through a channel, into a distal part ofthe endoscope.
 12. The method according to claim 11, wherein theendoscope is a medical endoscope.